DESCRIPTION: Bone mineral density (BMD) currently is the most widely invoked paradigm for fracture risk assessment in osteoporosis although it accounts for only a fraction of the bone's strength. There is therefore a compelling need for noninvasive assessment of bone quality in terms of cancellous bone structure which, so far, required transiliac bone biopsy. The long term goal of the proposed work is the development of the noninvasive bone biopsy providing, in a single integrated examination, a quantitative profile of bone quality. The hypothesis underlying this proposal is (i) that trabecular bone structure can be quantified noninvasively by means of magnetic resonance microimaging in vitro and in vivo; (ii) that trabecular bone architecture is a better predictor of bone strength and thus fracture risk than conventional bone densitometry; (iii) that there is a relationship between structure and the induced local magnetic field obtained from a direct measurement of the line broadening parameter R2' (1/T2*-1/T2). It is, further hypothesized that the targeted measurement site - the radius - is uniquely suited for assessing bone quality since (i) it is known to be predictive of fractures of the hip and spine; (ii) its peripheral location and physical size permits micro-imaging at high SNR and resolution. The specific aims consist of technical, experimental and clinical components: 1. Further develop and refine 3D micro-imaging techniques for operation at 4 Tesla field strength; including algorithms conceived by the investigators for image-based characterization of the three-dimensional trabecular network. 2. Evaluate the three-dimensional microstructure of the trabeculae by 3D micro-imaging of intact cadaveric radii and measure the structure-induced line broadening (R2') of the bone marrow signal to ascertain its relationship with structural parameters. 3. Measure both trabecular microstructure and R2' by means of the techniques specified in Aims #1 and #2 in the wrist of patients with postmenopausal and corticosteroid-induced osteoporosis, and their age-matched controls and determine whether the two quantitative MR techniques can discriminate the three groups.